Fermentation process for producing monosaccharides in free form from nucleotide-activated sugars

ABSTRACT

The present invention relates to a process for producing a monosaccharide, e.g. L-fucose, in free form using a microbial fermentation process. The used microorganism exhibits hydrolase activity on nucleotide-activated sugars and releases the monosaccharide in an unmodified free form. The free monosaccharide is retrieved from the supernatant of the cultivated microorganism.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of U.S. application Ser. No.15/546,778, filed Jul. 27, 2017, which is a National Stage entry ofInternational Application No. PCT/EP2016/051919, filed Jan. 29, 2016,which claims to European Patent Application No. 15153383.3, filed Jan.30, 2015.

REFERENCE TO SEQUENCE LISTING SUBMITTED AS A COMPLIANT ASCII TEXT FILE(.txt)

Pursuant to the EFS-Web legal framework and 37 CFR §§ 1.821-825 (seeMPEP § 2442.03(a)), a Sequence Listing in the form of an ASCII-complianttext file (entitled “Sequence_Listing_3000045-001001_ST25.txt” createdon 18 Jul. 2019, and 19,783 bytes in size) is submitted concurrentlywith the instant application, and the entire contents of the SequenceListing are incorporated herein by reference.

BACKGROUND Field

The present invention relates to a microbial fermentation process forproducing a monosaccharide of interest in free form fromnucleotide-activated sugars.

Description of Related Art

Carbohydrates play roles in all forms of life by taking on vital rolesin energy storage, structural function, signalling, information storageetc. For this task nature synthesizes several major monosaccharides likeglucose, N-acetyl-glucosamine, mannose, N-acetyl-mannosamine, fructose,fucose, ribose, sialic acid, xylose etc. and several minor ones for morespecialized applications, like for example D-allose.

L-fucose (6-deoxy-L-galactose) and fucosylated oligo-, andpolysaccharides are of great interest for the chemical, cosmetic andpharmaceutical industry since they have high potential for nutritionaland biomedical applications (Hauber, H.-P., Schulz, M., Pforte, A.,Mack, P., Zabel, P. & Schumacher, U. (2008) Inhalation with fucose andgalactose for treatment of Pseudomonas aeroginosa in cyctric fibrosispatients. Int. J. Med. Sci. 5, 371-376; Isnard, N., Bourles-Dagonet F.,Robert, L. & Renard, G. (2005) Studies on corneal wound healing: Effectsif fucose on iodine vapor-burnt rabbit corneas. Ophthalmologica 219,324-333; Robert, L., Fodil-Bourahla, I., Bizbiz, L. & Robert, A. M.(2004) Effect of L-fucose and fucose-rich polysaccharides on elastinbiosynthesis, in vivo and in vitro. Biomed. Pharmacother. 58, 123-128;Wild, M. K., Lühn, K., Marquardt, T. & Vestweber, D. (2002) Leukocyteadhesion deficiency II: therapy and genetic defect. Cells Tissues Organs172, 161-173; Adam, E. C., Mitchell, B. S., Schumacher, D. U., Grant, G.& Schumacher, U. (1997) Pseudomonas aeruginosa II lectin stops humanciliary beating: therapeutic implications of fucose. Am. J. Respir. CareMed. 155, 2102-2104). They are known to have anti-inflammatory,anti-viral, and anti-tumor properties and also act as prebiotics. Due tothe anti-aging effect L-fucose is also of interest for cosmetics(Isnard, N., Fodil-Bourathla, I., Robert A. M. & Robert, L. (2004)Pharmacology of skin aging. Stimulation of glycosaminoglycanbiosynthesis by L-fucose and fucose rich polysaccharides, effect of invitro aging of fibroblasts. Biomed. Pharmacother. 58, 202-204). Inaddition fucosylated derivatives are known for their antiallergic andemulsifying properties.

Whereas some monosaccharides can be obtained from nature in largeamounts and at reasonable cost (e.g. glucose, N-acetylglucosamine, andfructose), most monosaccharides are rather scarce and can be found innature only in small amounts, like for example L-fucose(6-deoxy-L-galactose).

For commercial production of monosaccharides, almost exclusivelyoligosaccharides obtained from nature are used as sources. Theseoligosaccharides are acid hydrolyzed and from the releasedmonosaccharides the individual sugars are purified. Due to the highchemical similarity of the monosaccharides (mostly differing from eachother only by the orientation of individual hydroxyl-groups) theseparation of individual monosaccharides in pure form is ratherlaborious and costly.

L-fucose represents such a rare sugar, which is currently obtained viathe hydrolysis of complex oligosaccharides, either from algae orbacterial origin. For the purification of individual monosaccharidesfrom complex hydrolysates often noxious chemical have to be employed,like for example lead acetate and excessive amounts of organic solvents(Schweiger, R. G. (1966) Preparation of α-L-fucosides and L-fucose fromfucoidan. U.S. Pat. No. 3,240,775). Therefore, the isolation ofindividual monosaccharides from a complex hydrolysate ofoligosaccharides is challenging (due to the high chemical similarity ofthe individual monosaccharides released) and environmentally harmful(due to the excessive use of toxic chemicals, such a lead carbonate).Also the availability of oligosaccharides rich in a certain sugar can berather restricted in nature and also highly variable due to seasonalchanges. L-Fucose represents such a scare monosaccharide which istraditionally obtained by the acid hydrolysis of fucose-containingpolysaccharides. Fucose is mainly derived from the polysaccharidefucoidan, a fucan monosulfate present in all common brown seaweedscomprising the families Fucaceae and Laminariaceae (Black, W. A. P(1954): The seasonal variation in the combined L-fucose content of thecommon british Laminariaceae and Fucaceae. J. Sci. Food Agric. 5,445-448). Today, L-fucose is obtained in large quantities mainly by thecollection of brown seaweed belonging to the family Fucaceae, which canbe found world-wide but in high amounts at the European shores of theAtlantic Ocean. The large-scale harvest of brown seaweed from sea shorescauses environmental concerns and is limited by environmental protectionlaws.

For example, JP 2000351790 discloses a method for extracting fucoidanand for obtaining and separating a fucose-containing oligosaccharidefrom the extracted fucoidan.

Besides the hydrolysis of fucoidan from brown-seaweed recently a patentpublication showed that L-fucose can also be obtained via the hydrolysisof natural occurring L-fucose containing bacterial polysaccharides: WO2012/034996 A1 discloses a strain belonging to the Enterobacteriaceaefamily, which strain is able to produce extracellular polysaccharideswhich contain L-fucose. For the production of L-fucose, thepolysaccharides produced by the strain are recovered and subjected tohydrolysis, e.g. by treatment with sulphuric acid or trifluoroaceticacid.

WO 2014067696 A1 describes for the first time a process for productionof L-fucose by using a recombinant microorganism that possesses aglycosyltransferase and a glycosidase which work together to synthesizeL-fucose in a free form. This process needs two enzymes and an acceptormolecule. The glycosyltransferase catalyses the transfer of fucose fromGDP-L-fucose to the acceptor, for example lactulose, to synthesizefucosyllactulose. The Fucosylated acceptor (e.g. Fucosyllactulose) isthen hydrolysed by a glycosidase into the acceptor molecule andL-fucose. The acceptor is then again available for fucosylation by theemployed fucosyltransferase. L-fucose is then liberated from the cell byexport into the medium were it can be retrieved from the supernatant. Bythis means the feedback inhibition of the GDP-fucose pathway can beeasily overcome and significant (several g/I) amounts of free L-fucosecan be obtained by microbial fermentation.

Besides the extraction of L-fucose from poly- or oligosaccharidehydrolysates, several synthetic routes for L-fucose have been developedstarting from other monosaccharides, like L-arabinose, D-galactose,L-rhamnose, D-mannose and D-glucose. With the most efficient syntheticroute developed by Defraye et al (1984) starting from the raremonosaccharide L-rhamnose (Defaye, J., Gadelle, A. & Angyal, S. (1984)An efficient synthesis of L-fucose and L-(4-²H)fucose. Carbohydr. Res.126, 165-169). Generally the yields of these chemical syntheses areoften rather poor and involve several chemical steps. Besides involvingseveral synthetic steps, extensive protection group chemistry has to beused for the chemical synthesis of L-fucose. In general, the large-scalechemical synthesis of monosaccharides have not proved economical viablein comparison to extraction of L-fucose from polysaccharides collectedfrom nature.

Thus, currently, the preparation of any monosaccharide in pure formrequires a significant effort in the purification of othermonosaccharides away from the target monosaccharide, often involvinglarge volumes of organic solvents and other noxious chemicals. As aconsequence, the exclusive accumulation of a single desiredmonosaccharide, like for example L-fucose, would be of immense help.However most microorganisms are restricted in the kinds ofmonosaccharides they are able to utilize. In addition, they often exertstrong preferences towards certain monosaccharides in case that severalmonosaccharides are available at the same time as carbon source.

SUMMARY

In view of the above, it is an object of the present invention toprovide a new process for the production of a single desiredmonosaccharide in free form, by means of which the monosaccharide can beretrieved fast and efficiently, i.e. in large scale and cost-effectivelyand without negative environmentally effects.

This and other objects are achieved by a process for producing, in largescale, a monosaccharide of interest in free form using a microorganism,the process comprising the steps of:

a.) providing a microorganism for the synthesis of the monosaccharidecomprising an enzyme capable of catalyzing the hydrolysis of anucleotide-activated monosaccharide to release the monosaccharide ofinterest from the nucleotide-activated monosaccharide, and

b.) cultivating the microorganism in a medium suitable for growing themicroorganism, wherein the microorganism is unable to metabolize themonosaccharide to a significant extent, so that the monosaccharide ofinterest is produced and accumulates during cultivation step in freeform.

The object underlying the invention is completely solved in this way.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT

Applicant's above process has not previously been described, utilizes amicroorganism comprising and expressing an enzyme that hydrolyses anucleotide-activated monosaccharide and accumulates the freemonosaccharide. The enzyme possessing hydrolysing activity onnucleotide-activated sugars can be, e.g., a fucosyltransferase,preferably a variant of the alpha-1,2-fucosyltransferase encoded by thewbgL gene of E. coli:O126 (acc. No. ADN43847) or the1,2-fucosyltransferase futC from Helicobacter pylori (acc. No.AAD29868). Although unmodified microorganisms having the above describedenzymatically features can be employed within the present invention,according to one aspect of the invention, the microorganism is arecombinant microorganism, wherein the recombinant microorganism hasbeen transformed to comprise and express at least one nucleic acidsequence not naturally occurring in the microorganism and encoding anenzyme capable of catalyzing the hydrolysis of a nucleotide-activatedmonosaccharide.

In contrast to prior processes, a single enzyme capable of catalyzingthe hydrolysis of, i.e. hydrolyzing, nucleotide-activated sugars, i.e.monosaccharides, is used to release the monosaccharide, whereas previousprocesses known in the art, employ at least one enzyme transferring themonosaccharide from a donor substrate to an acceptor substrate with asubsequent step of releasing the monosaccharide from the acceptor bymeans of a glycosidase. This step is not necessary in the presentinvention thereby facilitating the process for producing amonosaccharide of interest. Accordingly, in the process according to theinvention, an enzyme is used that is capable of catalyzing thehydrolysis of nucleotide-activated monosaccharides and releasing themonosaccharide in free form “in the absence of an acceptor”. Also,according to the invention, the process according to the invention isrun without the targeted use of a glycosidase capable for releasing themonosaccharide from an acceptor-substrate.

With the newly provided process and the newly providedmicroorganism—recombinant or not—, it is possible to produce a desiredmonosaccharide in a free form and in large amounts, withoutnecessitating chemicals or elaborate process steps. The processaccording to the invention represents a microbial fermentation process,suitable for getting employed for industrial large scale production ofrare or other monosaccharides, which can be readily retrieved from themedium the microorganism is cultivated in.

The expression “monosaccharide” as used herein and as generallyunderstood in the field of the invention, refers to the most basic unitof carbohydrates. Monosaccharides are the simplest form of sugar and areusually colourless, water-soluble, crystalline solids. Examples ofmonosaccharides include glucose, fructose, galactose, xylose, mannose,fucose, rhamnose and ribose. Monosaccharides are the building blocks ofdisaccharides such as sucrose and polysaccharides such as cellulose andstarch. “Oligosaccharide” as the term is used herein and as generallyunderstood in the state of the art, refers to a saccharide polymercontaining two monosaccharides or more.

The term “nucleic acid sequence encoding . . . ” generally refers to anypolyribonucleotide or polydeoxyribonucleotide, which may be unmodifiedRNA or DNA or modified RNA or DNA, and generally represents a gene whichencodes a certain polypeptide or protein. The term includes, withoutlimitation, single- and double-stranded DNA, DNA that is a mixture ofsingle- and double-stranded regions or single-, double- andtriple-stranded regions, single- and double-stranded RNA, and RNA thatis mixture of single- and double-stranded regions, hybrid moleculescomprising DNA and RNA that may be single-stranded or, more typically,double-stranded, or triple-stranded regions, or a mixture of single- anddouble-stranded regions. The term also encompasses polynucleotides thatinclude a single continuous region or discontinuous regions encoding thepolypeptide (for example, interrupted by integrated phage or aninsertion sequence or editing) together with additional regions thatalso may contain coding and/or non-coding sequences.

In this context, the term “polypeptide(s)” refers to any peptide orprotein comprising two or more amino acids joined to each other bypeptide bonds or modified peptide bonds. “Polypeptide(s)” refers to bothshort chains, commonly referred to as peptides, oligopeptides andoligomers and to longer chains generally referred to as proteins.Polypeptides may contain amino acids other than the 20 gene encodedamino acids. “Polypeptide(s)” include those modified either by naturalprocesses, such as processing and other post-translationalmodifications, but also by chemical modification techniques. It will beappreciated that the same type of modification may be present in thesame or varying degree at several sites in a given polypeptide, withoutessentially altering the activity of the polypeptide. Also, a givenpolypeptide may contain many types of modifications. Modifications canoccur anywhere in a polypeptide, including the peptide backbone, theamino acid side-chains, and the amino or carboxyl termini.

In the present invention the term “nucleotide-activated monosaccharide”used in combination with the “enyzme capable of catalyzing thehydrolysis of a nucleotide-activated monosaccharide”, or “enzyme capableof hydrolysing a nucleotide-activated monosaccharide”, describes anenzyme possessing catalytic activity on nucleotide-activatedmonosaccharides; hydrolysis leads to release of the desiredmonosaccharide. In this connection, the term “glycosyltransferase”designates and encompasses enzymes that catalyse the transfer ofmonosaccharide moieties from an activated nucleotide monosaccharide (the“glycosyl donor”) to a glycosyl acceptor molecule. In the presentinvention, the glycosyltransferase used in the process and microorganismaccording to the invention does calatyze the hydrolysis of thenucleotide-activated monosaccharide in absence of the acceptor molecule.According to one aspect of the invention, it is particularly preferredif the nucleotide-activated sugar hydrolase is a bacterialfucosyltransferase, and preferably a variant of thealpha-1,2-fucosyltransferase encoded by the wbgL gene of E. coli:0126(acc. No. ADN43847) or other fucosyltransferases catalysing hydrolysisof GDP-L-fucose in the absence of an acceptor molecule.

Accordingly, the term nucleotide-activated sugar hydrolase or a nucleicacid/polynucleotide encoding an nucleotide-activated sugar hydrolaserefer to an enzyme that catalyses hydrolytic cleavage ofnucleotide-activated sugars, such as GDP-fucose, UDP-galactose,GDP-mannose, GDP-rhamnose, and other nucleotide sugars naturallyoccurring. Preferably this nucleotide-activated sugar hydrolase is aglycosyltransferase that does not or predominantly not transfer themonosaccharide to an acceptor molecule. In the case of GDP-L-fucose, theenzyme capable of hydrolyzing a nucleotide-activated monosaccharide is afucosyltransferase, e.g. but not limited to, aalpha-1,2-fucosyltransferase.

More specific, it is preferred if the alpha-1,2-fucosyltransferase WbgLfrom E. coli:126 possessing the amino acid residues substitutionsasparagine 69 to serine, histidine 124 to alanine, glutamate 215 toglycine, and isoleucine 268 to proline, or the 1,2-fucosyltransferaseFutC from Helicobacter pylori or other fucosyltransferases exhibitinghydrolytic activity on GDP-L-fucose in the absence of an acceptormolecule is used.

Within the scope of the present invention, also nucleicacid/polynucleotide and polypeptide polymorphic variants, alleles,mutants, and interspecies homologs are comprised by those terms, thathave an amino acid sequence that has greater than about 60% amino acidsequence identity, 65%, 70%, 75%, 80%, 85%, 90%, preferably 91%, 92%,93%, 94%, 95%, 96%, 97%, 98% or 99% or greater amino acid sequenceidentity, preferably over a region of at least about 25, 50, 100, 200,or 300, or more amino acids, to the amino acid sequences of thealpha-1,2-fucosyltransferases encoded by the wbgL gene of E. coli:O126(acc. No. ADN43847) or futC of H. pylori (acc. No. AAD29868).

Additionally, the polypeptide of the hydrolysing enzyme may be alteredby additions or deletions of peptide sequences in order to modify itsactivity. For example, polypeptide sequences may be fused to the enzymespolypeptide in order to effectuate additional enzymatic activity.

In addition, genes encoding an enzyme capable of hydrolyzing anucleotide-activated monosaccharide may be altered so that the geneproducts include proteins or polypeptides that represent functionallyequivalent gene products. Such an equivalent hydrolase gene product maycontain deletions, additions or substitutions of amino acid residueswithin the amino acid sequence encoded by the hydrolase gene sequencedescribed above, but which results in a silent change, thus producing afunctionally equivalent gene product coding for an enzyme capable ofhydrolyzing a nucleotide-activated monosaccharide. Amino acidsubstitutions may be made on the basis of similarity in polarity,charge, solubility, hydrophobicity, hydrophilicity, and/or theamphipathic nature of the residues involved. For example, nonpolar(hydrophobic) amino acids include alanine, leucine, isoleucine, valine,proline, phenylalanine, tryptophan, and methionine; planar neutral aminoacids include glycine, serine, threonine, cysteine, tyrosine,asparagine, and glutamine; positively charged (basic) amino acidsinclude arginine, lysine, and histidine; and negatively charged (acidic)amino acids include aspartic acid and glutamic acid.

Within the context of this invention, “functionally equivalent”, as usedherein, refers to a polypeptide capable of exhibiting a substantiallysimilar in vivo hydrolase activity on nucleotide-activated sugars as theendogenous hydrolase gene product encoded by the hydrolase gene sequencedescribed above, as judged by any of a number of criteria, including butnot limited to antigenicity, i.e., the ability to bind to ananti-nucleotide-activated sugar hydrolase antibody, immunogenicity,i.e., the ability to generate an antibody which is capable of binding anucleotide-activated monosaccharide hydro-laseprotein or polypeptide, aswell as enzymatic activity. Accordingly, the present invention alsocomprises enzymes that are functionally equivalent to the onesspecifically disclosed.

Also, one skilled in the art will readily derive from the presentinvention, that any modification to the disclosed enzymes can be usedwithin the process and microorganism of the present invention, whichmodification is leading to an increased hydrolysing activity of thedescribed enzymes herein. Thus, such modified enzymes displaying anincreased hydrolysing activity compared to the unmodified form arecomprised by the invention as well.

Included within the scope of the invention are nucleotide-activatedsugar hydrolase proteins, polypeptides, and derivatives (includingfragments) which are differentially modified during or aftertranslation. Furthermore, non-classical amino acids or chemical aminoacid analogs can be introduced as a substitution or addition into theenzymes polypeptide sequence.

According to a preferred embodiment of the process according to theinvention, the enzyme is a variant of the 2-fucosyltransferase encodedby the wbgL gene, or a variant of the 1,2-fucosyltransferase encoded bythe futC gene from Helicobacter pylori, the variant carrying at leastone, preferably at least two, and more preferably more than twomodifications as compared to the wild type 2-fucosyltransferase encodedby the wbgL gene or to the wild type 1,2-fucosyltransferase encoded bythe futC gene, respectively, the modification leading to an increasedhydrolizing activity of the enzyme.

The enzyme capable of hydrolyzing nucleotide-activated sugars may beproduced by recombinant DNA technology using techniques well known inthe art. Methods which are well known to those skilled in the art can beused to construct expression vectors containing enzyme coding sequencesand appropriate transcriptional translational control signals thatpermit synthesis of an enzyme catalysing hydrolysis ofnucleotide-activated sugars. These methods include, for example, invitro recombinant DNA techniques, synthetic techniques, and in vivogenetic recombination. See, for example, the techniques described inSambrook, J. and Russell D. W. (1989) Molecular Cloning: A LaboratoryManual, 2nd Ed., Cold Spring Harbor Laboratory Press, Cold SpringHarbor, N.Y.

According to an embodiment of the process according to the invention theat least one modification is at least one an amino acid substitution.According to another embodiment, the modification is or comprises atleast one, two or more than two, in particular three, four, five, six,seven, eight, nine, or ten amino acids substitutions, wherein themodified enzyme capable of hydrolyzing a nucleotide-activatedmonosaccharide has an increased hydrolyzing activity on thenucleotide-activated monosaccharide compared to the unmodified wild-typeenzyme.

According to one embodiment, it is preferred if thealpha-1,2-fucosyltransferase WbgL from E. coli:126 possessing the aminoacid residues substitutions asparagine 69 to serine, histidine 124 toalanine, glutamate 215 to glycine, and isoleucine 268 to proline, or the1,2-fucosyltransferase FutC from Helicobacter pylori or otherfucosyltransferases exhibiting hydrolytic activity on GDP-L-fucose inthe absence of an acceptor molecule is used.

One skilled in the art will appreciate from the disclosure of thisinvention, that not only the specific substitutions as specified above,but also other modifications of these specifically described enzymes, inparticular other substitutions are encompassed by this invention, aslong as the accordingly modified enzyme has an increased hydrolyzingactivity on the nucleotide-activated monosaccharide compared to theunmodified wild-type enzyme. Alternative substitutions, which can besuitable, are also discussed above more generally, but should be appliedhere also.

Presently, and throughout the invention, “recombinant” means geneticallyengineered DNA prepared by transplanting or splicing genes from onespecies into the cells of a host microorganism of a different species.Such DNA becomes part of the host's genetic makeup and is replicated.

“Microorganism” presently designates and encompasses any microscopicorganism that comprises either a single cell, cell clusters, ormulticellular relatively complex organisms, which is suitable to beemployed in the process according to the invention, and particularlyincludes bacteria and yeast. A microorganism as employed according tothe invention can be cultivated in a liquid medium, and generally needsa carbon source in the medium to grow and replicate.

Consequently, “a recombinant host microorganism” is designated to meanany microorganism containing, a nucleic acid sequences coding for aglycosyltransferase or nucleotide-activated sugar hydrolase, or codingfor a fucosyltransferase or a GDP-L-fucose hydrolase, wherein thenucleic acid sequences coding for these enzymes are nucleic acidsequences foreign to/not naturally occurring in the recombinant (host)cell and wherein the foreign/not naturally in said microorganismoccurring sequence is integrated in the genome of the host microorganismcell. Thereby, “not naturally occurring” means that the nucleic acidsequence is foreign to said host microorganism cell, i.e. the nucleicacid sequences are heterologous with respect to the microorganism hostcell. The heterologous sequence may be stably introduced, e.g. bytransfection, transformation, or transduction, into the genome of thehost microorganism cell, wherein techniques may be applied which willdepend on the host cell the sequence is to be introduced. Varioustechniques are known to a person skilled in the art and are, e.g.,disclosed in Sambrook et al., 1989, supra. Thus, the host cell theheterologous sequence has been introduced in, will produce theheterologous proteins the nucleic acid sequences according to theinvention are coding for.

For recombinant production, host cells can be genetically engineered toincorporate expression systems or portions thereof and the nucleic acidsequences of the invention. Introduction of a nucleic acid sequence intothe host microorganism cell can be effected by methods described in manystandard laboratory manuals, such as Davis et al., Basic Methods inMolecular Biology, (1986), and Sambrook et al., 1989, supra.

Thus, the nucleic acid sequences according to the invention, may, e.g.,be comprised in a vector which is to be stably transformed/transfectedinto host microorganism cells.

A great variety of expression systems can be used to produce thepolypeptides of the invention. Such vectors include, among others,chromosomal, episomal and virus-derived vectors, e.g., vectors derivedfrom bacterial plasmids, from bacteriophage, from transposons, fromyeast episomes, from insertion elements, from yeast chromosomalelements, from viruses, and vectors derived from combinations thereof,such as those derived from plasmid and bacteriophage genetic elements,such as cosmids and phagemids. The expression system constructs maycontain control regions that regulate as well as engender expression.Generally, any system or vector suitable to maintain, propagate orexpress polynucleotides and to synthesise a polypeptide in a host may beused for expression in this regard. The appropriate DNA sequence may beinserted into the expression system by any of a variety of well-knownand routine techniques, such as, for example, those set forth inSambrook et al., supra.

As used herein, the term “recovering” means isolating, harvesting,collecting or otherwise separating from the microorganism culture themonosaccharide produced by the microorganism according to the invention.

According to a preferred embodiment of the process according to theinvention, the microorganism is further modified to have inactivated orseverely reduced or to lack catabolic pathways leading to thedegradation of the produced monosaccharide.

According to yet another embodiment, the microorganism is furthermodified to have inactivated or severely reduced or to lack genesinvolved in the catabolism of L-fucose.

According to another embodiment, the microorganism is further modifiedto overexpress at least one gene involved in the biosynthesis of thenucleotide-activated monosaccharide to improve supply of thenucleotide-activated monosaccharide of the monosaccharide. In thisregard it is preferred if the at least one gene is heterologous orhomologous.

According to another embodiment of the process according to the presentinvention, at least one gene involved in the biosynthesis of GDP-fucose,GDP-mannose or GDP-rhamnose is overexpressed to improve supply ofGDP-fucose, GDP-mannose or GDP-rhamnose, respectively. In this regard itis preferred if the at least one gene is heterologous or homologous.

According to another embodiment of the process according to the presentinvention, the microorganism is further modified to have inactivated orreduced competing pathways for the nucleotide-activated monosaccharide.

According to another embodiment of the process according to the presentinvention, the microorganism is further modified to express aphosphatase, in case where the monosaccharide is released in aphosphorylated form by the enzyme.

Throughout the invention, it is particularly preferred if the freemonosaccharide to be produced is selected from L-fucose, L-rhamnose orL-mannose.

In a preferred embodiment, the microorganism is cultivated in a mediumcontaining a carbon source that is selected from glycerol, sucrose,acetate, glucose, fructose, molasses, lactose, xylose, cellulose,syngas, carbon dioxide or carbon monoxide. In this context it is to beunderstood that any other—preferably low-cost—fermentation substratescan be employed as carbon source, and the person skilled in the art willreadily able to employ a carbon source suitable within the presentinvention in order to grow the microorganism to produce the desiredmonosaccharide in large-scale.

According to one aspect of the invention, a carbon source is constantlyadded to the medium during the cultivating step of the microorganism,e.g. a recombinant microorganism.

By constantly adding the carbon source during the cultivation step, aconstant and effective production of the monosaccharide is accomplished.

According to another aspect of the invention, the monosaccharide isrecovered from supernatant of the cultivated recombinant hostmicroorganism, which supernatant is obtained by centrifuging thecultivated host microorganism to obtain a supernatant and a hostmicroorganism pellet.

With the newly provided process, it is possible to retrieve the producedmonosaccharide from the medium the host microorganism is cultivated in,since the monosaccharide which is produced in a microorganism cell istransported into the medium, thus making it effortlessly possible torecover the monosaccharide from the supernatant, once the cells of themicroorganism have been separated from the cultivation medium.

Other mono-, or oligosaccharides which may be produced in themicroorganism during the synthesis of the desired the monosaccharide,and which mono-, or oligosaccharides impair/interfere with therecovering/purification step of the desired monosaccharide, can bemetabolised by the microorganism, so that the recovering step of thedesired monosaccharide is further improved and facilitated. Thereforesaccharide metabolising enzyme(s)) may be externally added/supplied tothe medium at the end of the process according to the invention. Indoing so, undesired sugars cannot accumulate and do not interfere withthe recovering of the desired monosaccharide. Genes encoding metabolicpathways or enzymes can be expressed in the microorganism in order tometabolize otherwise interfering undesired monosaccharides, and oneskilled in the art will—upon reading the invention—readily recognizeother suitable pathways or enzymes to deregulate/activate or supply,which will depend from the monosaccharide to be produced.

According to another aspect of the invention, the process according tothe invention comprises the following steps:

-   -   a) providing, in a medium suitable for growing a microorganism,        a recombinant host microorganism which has been transformed to        comprise a nucleic acid sequence encoding an enzyme catalysing        hydrolysis of nucleotide-activated monosaccharide not naturally        occurring in the microorganism wherein the microorganism is        unable to metabolize the monosaccharide to be produced in        significant amounts,    -   b) cultivating the recombinant host microorganism in said medium        whereby the monosaccharide is produced in a free form,    -   c) recovering the free monosaccharide from the medium.

Thus, the process as described in the above paragraphs comprises theadditional step of recovering the free monosaccharide from the medium.

According to another aspect of the invention, there is disclosed andclaimed a microorganism

The definitions used and set forth above for specific terms inconnection with the process do also apply for the recombinantmicroorganism presented therein.

According to a preferred embodiment, the microorganism—used in theprocess according to the invention and claimed therein—is selected froma bacterial or yeast strain able synthesize nucleotide-activated sugarsfrom which the desired monosaccharide can be obtained by hydrolyticcleavage of the nucleotide-activated monosaccharide. The bacteriumEscherichia coli, Corynebacterium glutamicum and the yeast Saccharomycessp. have the advantage that these microorganisms can be grown easily andinexpensively in laboratory settings, and the bacterium and yeast havebeen intensively investigated for over many years.

Accordingly, in a preferred embodiment, the host microorganism used inthe process according to the invention and otherwise claimed therein isselected from the group consisting of bacteria and yeast, and ispreferably an Escherichia coli strain.

It is further preferred in an embodiment of the present invention, ifthe recombinant host microorganism is further modified to lack genescoding for enzymes involved in the metabolism of the desiredmonosaccharide, in the case of L-fucose as desired monosaccharide genesencoding L-fuculosose kinase, L-fucose isomerase, fuculose-1-phospatealdolase, and UDP-glucose:undecaprenyl-phosphate glucosephosphotransferase. In addition, and according to a preferredembodiment, glycosyltransferase genes using the nucleotide-activatedmonosaccharide as substrate for the synthesis of polysaccharides (e.g.fucosyltransferases, or enzymes involved in the synthesis of fucosylatedoligosaccharides such as colonic acid) are deleted.

Additionally, overexpression of genes improving synthesis ofnucleotide-activated sugars is preferred. In the case of GDP-L-fucosegenes encoding phosphomannomutase (mane), mannose-1-phosphateguanosyltransferase (manC), GDP-mannose-4,6-dehydratase (gmd), andGDP-L-fucose synthase (wcaG) from E. coli or adequate genes from otherorganisms are overexpressed in the respective microorganism.

This embodiment has the advantage that intracellular degradation of theproduced monosaccharide L-fucose and production of colonic acid isprevented and synthesis of GDP-L-fucose is improved.

In another preferred embodiment, the recombinant host microorganism isfurther transformed to contain genes enabling the recombinant hostmicroorganism to grow on sucrose or glycerol as sole carbon source, andit is particularly preferred if the csc-gene cluster of Escherichia coliW (acc. No. CP0021851) is integrated into the genome of the hostmicroorganism, which gene cluster comprises the genes sucrose permase,fructokinase, sucrose hydrolase, and a transcriptional repressor (genescscB, cscK, cscA, and cscR, respectively), that enable the transformedmicroorganism to grow on sucrose as sole carbon source.

In this connection it is noted that the embodiments listed as preferredfor the process according to the invention all do apply for the claimedmicroorganism, where applicable.

Accordingly, the present invention also relates to the use of amicroorganism possessing an enzyme catalysing the hydrolysis ofnucleotide-activated monosaccharide wherein the microorganism is unableto metabolize the monosaccharide, and the invention further relates tothe use of the recombinant microorganism according to the invention forthe production of a monosaccharide, in particular of L-fucose.

It is noted that the definitions set forth above for describing certainterms of the process according to the invention shall apply for themicroorganism, recombinant or unmodified, as claimed and describedherein.

Alternatively, the method for producing monosaccharides may be appliedon cell-free systems, whereby the enzyme according to the invention andsuitable substrates are mixed in an aqueous reaction medium. The enzymecan be utilized free in solution, or they can be bound or immobilized toa support such as a polymer and the substrate may be added to thesupport. The support may be, e.g., packed in a column.

In particular, the present invention relates to a process wherein arecombinant Escherichia coli strain is used as recombinant hostmicroorganism, wherein in the recombinant Escherichia coli strain theL-fucose isomerase gene, the L-fuculose kinase gene, and theUDP-glucose:undecaprenyl-phosphate glucose phosphotransferase have beendeleted, and wherein the recombinant Escherichia coli strain has beentransformed to comprise a) genes enabling the E. coli strain to grow onsucrose or glycerol as sole carbon source, the genes encoding,respectively, sucrose permase, fructokinase, sucrose hydrolase, and atranscriptional repressor, b) genes encoding phosphomannomutase,mannose-1-phosphate guanosyltransferase, GDP-mannose-4,6-dehydratase,and GDP-L-fucose synthase from E. coli or other organisms, c) a geneencoding an enzyme catalysing hydrolysis of nucleotide-activatedmonosaccharides, e.g. a fucosyltransferase that hydrolyses GDP-L-fucosein absence of an acceptor molecule. Further advantages follow from thedescription of the embodiments and the attached drawings.

It goes without saying that the abovementioned features and the featureswhich are still to be explained below can be used not only in therespectively specified combinations, but also in other combinations oron their own, without departing from the scope of the present invention.Also, it is noted that the particular features presented in thedependent claims can be combined with each other in other manners withinthe scope of the invention such that the invention should be recognizedas also specifically directed to other embodiments having any otherpossible combination of the features of the dependent claims.

FIGURES

Several embodiments of the invention are illustrated in the figures andexplained in more detail in the following description. In the figures:

FIG. 1 Detection of free L-fucose in the culture supernatant of an E.coli BL21(DE3) production strain containing a pDEST:wbgL library afterrandom mutagenesis of wbgL by error-prone PCR. Supernatants of culturesfrom E. coli BL21(DE3) production strain harboringpDEST:wbgL(error-prone) clones were applied to a colorimetric L-fucosedehydrogenase assay (for description of the assay see paragraph [0089]below). Well depicted as “WT” contained supernatant of an E. coliBL21(DE3) production strain pDEST:wbgL culture, expressing theunmodified wbgL gene. Wells signed “D1” and “H2” contained culturesupernatant from clones synthesizing WbgL variants (H124A E215G) (cloneD1) and WbgL (N69S I268P) (clone H2);

FIG. 2 LC-MS/MS analytics of culture supernatants of E. coli BL21(DE3)production strain harboring pDEST:wbgL(H124A E215G) (clone D1), andpDEST:wbgL(N69S I268P) (clone H2). 4.3 g/L, and 2.5 g/L L-fucose wereproduced by clones D1, and clone H2, respectively;

FIG. 3 Detection of L-fucose released from GDP-L-fucose by GDPL-fucosehydrolase activity. Cell lysates of E. coli BL21(DE3) pDEST:futC and E.coli BL21(DE3) pDEST:wbgL (H124A E215G) were applied to an in vitroGDP-L-fucose hydrolase assays containing 5 mM GDP-L-fucose. FreeL-fucose was detected in a colorimetric L-fucose dehydrogenase assay(for description of the assay see paragraph [0089] below). The assay inwell 1 contained 0.27 units FutC, in well 2 0.32 units WbgL (H124AE215G) were applied. To confirm stability of GDP-L-fucose the assay wasperformed with bovine serum albumin (well 3); and

FIGS. 4A-D The sequence of <P1e1-manCB-PT₅-gmd> (SEQ ID No: 1),wcaG-dhfr (FIG. 4A), <cscB-cscK-cscA-cscR> (SEQ ID No. 2) (FIG. 4B),<wbgL> (SEQ ID No. 3) (FIG. 4C), and <futC> (SEQ ID No. 4) (FIG. 4D).

EXAMPLES

Construction of a Fucose Producing E. coli Strain

Escherichia coli BL21 (DE3) (Novagen, Darmstadt, Germany) was used forgenetic manipulations to construct the fucose production strain. Sincefucose is produced by hydrolysis of GDP-L-fucose, synthesis ofGDP-L-fucose is enhanced by genomic integration and overexpression ofthe genes encoding phosphomannomutase (manB), mannose-1-phosphateguanosyltransferase (manC), GDP-mannose-4,6-dehydratase (gmd), andGDP-L-fucose synthase (wcaG) from E. coli K12 DH5α. The operon manC-manBis under transcriptional control of the P_(tet) promotor and the operongmd-wcaG is expressed from the P_(T5) promotor. The gene cluster<P_(tet)-manCB-P_(T5)-gmd, wcaG-dhfr> (SEQ ID No. 1; FIG. 4A) comprisesalso the dhfr gene, encoding a dihydrofolate reductase that conferstrimethoprim resistance to the integrants. For integration of thecluster into the E. coli BL21(DE3) genome by transposition, the clusteris flanked by inverted terminal repeats specifically recognized by themariner-family transposable element Himar1. In addition the csc-genecluster of E. coli W was introduced into the genome of the hostorganism. The gene cluster comprises the genes for sucrose permease(cscB), fructokinase (cscK), sucrose hydrolase (cscA), and atranscriptional repressor (cscR). Integration of the cluster<cscB-cscK-cscA-cscR> (SEQ ID No. 2; FIG. 4B) that was flanked by Himar1specific inverted terminal repeats was performed by Himar1 transpositionand mediates to the host organism the ability to grow on sucrose as solecarbon source (Choi, K.-H. and Kim, K.-J. (2009) Applications oftransposon-based gene delivery system in bacteria. J. Microbiol.Biotechnol. 19, 217-228).

To prevent GDP-L-fucose depletion by formation of colonic acid the genewcaJ predicted to encode a UDP-glucose:undecaprenyl phosphateglucose-1-phosphate transferase was deleted from the E. coli BL21(DE3)genome according to the method of Datsenko and Warner (Datsenko, K. A.and Warner B. L. (2000) One-step inactivation of chromosomal genes inEscherichia coli K-12 using PCR products. Proc. Natl. Acad. Sci. USA 97,6640-6645). The UDP-glucose:undecaprenyl phosphate glucose-1-phosphatetransferase catalyzes the first step in colonic acid synthesis(Stevenson, G., Andrianopoulos, K., Hobbs, M. and Reeves, P. R. (1996)Organization of the Escherichia coli K-12 gene cluster responsible forproduction of the extracellular polysaccharide colonic acid. J.Bacteriol. 178, 4885-4893). Additionally, the genes fucI and fucK of thefucose catabolic pathway, encoding the fucose isomerase and fuculosekinase, respectively, were inactivated by genomic knock-out to inhibitdegradation of L-fucose.

Cloning of the 2-Fucosyltransferases Genes wbgL and futC, andMutagenesis of wbgL

The 2-fucosyltransferase gene wbgL (SEQ ID No. 3; FIG. 4C) from E.coli:0126 (acc. No. AND43847) was codon-optimized and preparedsynthetically by GenScript Cooperation (Piscataway, USA). Also the futC(SEQ ID No. 4, FIG. 4D) gene encoding 1,2-fucosyltransferase fromHelicobacter pylori (acc. No. AAD29868) was synthetically synthesizedand codon optimized for expression in E. coli. For cloning into thevector pDEST14 the genes were amplified using primers 6128 (SEQ ID No.5) and 6129 (SEQ ID No. 6) for wbgL, and primers 6195 (SEQ ID No. 7) and6196 (SEQ ID No. 8) for futC, respectively; for primer sequences seetable 1 below:

TABLE 1 List of oligonucleotides used for polymerase chain reactionprimer Sequence 5′-3′ 6128 GGGGACAAGTTTGTACAAAAAAGCAGGCTTCGAAGGAGATACAACATGGGCAGCATTATTCGTCTGCAGGGTGG (SEQ ID No. 5) 6129GGGGACCACTTTGTACAAGAAAGCTGGGTTTAGCAGCTGCTATGTTTATCAACGTTGATC (SEQ ID No. 6) 6195GGGGACAAGTTTGTACAAAAAAGCAGGCTTCGAAGGAGGTAGAACATGGCCTTTAAAGTGGTTCAGATCTGCGGC (SEQ ID No. 7) 6196GGGGACCACTTTGTACAAGAAAGCTGGGTCCTATTACGCGTTATATTTCTGAGATTTCACTTCG (SEQ ID No. 8)

Mutations in the wbgL gene were introduced by several rounds oferror-prone PCR using the Diversify® PCR Random Mutagenesis Kit(Clonetech, Mountain View, USA) according to the manufacturesinstructions and primers 6128 and 6129. Purified error-prone PCRproducts were cloned into vector pDEST14 yieldingpDEST:wbgL(error-prone). Cloning into vector pDEST14 was generallyperformed using the Gateway technology (Gateway® Technology manual (LifeTechnologies, Carlsbad, USA)). Sequencing of the plasmids was performedby LGC Genomics (Berlin, Germany). Recombinant plasmids were transformedin suitable E. coli hosts by electroporation.

Growth Media and Cell Cultivation

The E. coli BL21(DE3) production strain harboring thepDEST:wbgL(error-prone) plasmid library was grown in mineral saltsmedium with 1% (v/v) glycerol and 1% (v/v) sucrose as carbon sources.The medium consists of 2 g/L NH₄H₂PO₄, 7 g/L K₂HPO₄, 2 g/L KOH, 0.3 g/Lcitric acid, 0.98 g/L MgSO₄×7 H₂O, and 0.02 g/L CaCl₂×6 H₂O. It issupplemented with one milliliter per liter trace element solution (54.4g/L ammonium ferric citrate, 9.8 g/L MnCl₂×4 H₂O, 1.6 g/L CoCl₂×6 H₂O, 1g/L CuCl₂×2 H₂O, 1.9 g/L H₃BO₃, 9 g/L ZnSO₄×7 H₂O, 1.1 g/L Na₂MoO₄×2H₂O, 1.5 g/L Na₂SeO₃, 1.5 g/L NiSO₄×6 H₂O). For selection 10 μg/mLtrimethoprim and 100 μg/mL ampicillin were added. Cells were grown in96-well microtiter plates for 24 hours at 30° C. with shaking. 50 μl ofthe preparatory cultures were transferred to 96-well plates with 400 μlfresh HEPES (100 mM) buffered medium containing 0.3 mM IPTG to induceexpression of wbgL genes in pDEST. Induced cultures were grown for twodays at 30° C. with shaking. Cells were sedimented by centrifugation andthe supernatant was used for detection of free L-fucose.

E. coli BL21(DE3) containing pDEST: wbgL (H124A E215G) and pDEST:futC,respectively, was grown in 2YT broth (Sambrook, J. and Russell D. W.(1989) Molecular Cloning: A Laboratory Manual, 2nd Ed., Cold SpringHarbor Laboratory Press, Cold Spring Harbor, N.Y.) at 30° C. to an OD600nm of 0.3 in the presence of 100 μg/mL ampicillin. Transcription of wbgL(H124A E215G) and futC was induced by addition of 0.3 mM IPTG. Cellswere harvested by centrifugation 20 h after induction. Cells were usedfor analysis of in vitro GDP-L-fucose hydrolase activity.

Enzyme Assays to Detect Free L-Fucose and In Vitro GDP-L-FucoseHydrolase Activity

Free L-fucose was measured in a colorimetric assay using L-fucosedehydrogenase (FuDH) from Pseudomonas sp. No. 1143 (acc. no. D32042)that catalyzes the NADP-dependent transformation of L-fucose toL-fucono-1,5-lactone. In the colorimetric assay nitroblue tetrazolium inthe presence of phenazine methosulfate is reduced to a blue-purpleformazan by NADPH. Formation of the formazan is monitored at 571 nm.(Mayer, K. M. and Arnold, F. H. (2002) A Colorimetric Assay to QuantifyDehydrogenase Activity in Crude Cell Lysates. J. Biomol. Screen. 7,135-140).

The fuDH gene from Pseudomonas sp. No. 1143 was overexpressed in E. coliBL21(DE3). The recombinant FuDH protein that contained an N-terminalHis6-tag was enriched from crude extract by immobilized-metal affinitychromatography using a Ni Sepharose™ 6 Fast Flow column (GE Healthcare,Pollards Wood, UK).

To detect free L-fucose in cultures of the fucose E. coli BL21(DE3)production strain harboring pDEST:wbgL(error-prone) each 200 μl L-fucosedehydrogenase assay reaction contained 50 μl cell culture supernatantand 150 μl of reagent solution that consists of 0.8 mM NADPH, 0.3 mMnitroblue tetrazolium, 0.03 mM phenazine methosulfate and 4.7 UnitsHis6-FuDH in 50 mM Tris (pH 8.0) with 0.13% (w/v) gelatin (all chemicalswere purchased from Sigma Aldrich, St. Louis, USA). Formation of theblue-purple formazan was measured after 10 min incubation at roomtemperature at 571 nm.

To detect GDP-L-fucose hydrolase activity in cell lysates of E. coliBL21(DE3) pDEST:wbgL (H124A E215G) and E. coli BL21(DE3) pDEST:futCcells were resuspended in 50 mM HEPES buffer (pH 7.5) with 5 mM MnCl₂and disrupted using glasbeats and a Mini-Beatbeater (BioSpec Producs,Bartlesville, USA). L-fucose was cleaved from GDP-L-fucose in aGDP-L-fucose hydrolase assay. 200 μl of the hydrolase assay contained12.5 μl of 100 mM GDP-L-fucose (Sigma Aldrich, St. Louis, USA) in 50 mMHEPES buffer (pH 7.5), 5 mM MnCl₂ and 50 μl cell free extract.

To verify stability of GDP-L-fucose the hydrolase assay was alsoperformed with 50 μl bovine serum albumin (30 mg/mL) instead of crudeextract. Protein concentrations were estimated according to Bradfordusing a commercially available dye solution (Roti-Quant®, Carl Roth,Karlsruhe, Germany). After one hour incubation at 30° C. the enzymes inthe GDP-L-fucose assays were inactivated by heating to 95° C. for 10min. 50 μl of the GDP-L-fucose hydrolase assay reaction mixture wereused to detect free L-fucose using the L-fucose dehydrogenase assay.This assay was set up as described above and incubated for 24 h at roomtemperature.

LC-MS/MS Analysis

Mass spectrometry analysis was performed by MRM (multiple reactionmonitoring) using a LC Triple-Quadrupole MS detection system (ShimadzuLC-MS 8050) (Shimadzu Corporation, Kyoto, Japan). Precursor ions areselected and analyzed in quadrupole 1, fragmentation takes place in thecollision cell using argon as CID gas, selection of fragment ions isperformed in quadrupole 3.

Chromatographic separation of fucose and maltotriose after dilution ofculture supernatant and reaction mixture from in vitro assay,respectively, 1:100 with 10 μg/mL maltotriose in H₂O (LC/MS Grade), wasperformed on a XBridge Amide HPLC column (3.5 μm, 2.1×50 mm (Waters,USA) with a XBridge Amide guard cartridge (3.5 μm, 2.1×10 mm) (Waters,USA). The HPLC system consists of a Shimadzu Nexera X2 SIL-30AC_(MP)Autosampler run at 8° C., a Shimadzu LC-20AD Pump, and a ShimadzuCTO-20AC column oven that was run at 30° C. (Shimadzu Corporation,Kyoto, Japan). The mobile phase was composed of acetonitrile:H₂O (62:38%(v/v)) with 10 mM ammonium acetate. A 1 μl sample was injected into theinstrument; the run was performed for 3 min with a flow rate of 300μl/min. L-fucose and maltotriose (added as internal standard fornormalization) were analyzed by MRM in ESI negative ionization mode. Themass spectrometer was operated at unit resolution. Fucose forms an ionof m/z 163.2 [M-H] and maltotriose an ion of m/z 503.2 [M-H]. Theprecursor ion of L-fucose was further fragmented in the collision cellinto the fragment ions m/z 88.9, m/z 70.8 and m/z 58.9. The molecularion of maltotriose (m/z 503.2) was fragmented into m/z 341.1, m/z 161.05and m/z 100.9. Collision energy, Q1 and Q3 Pre Bias were optimized foreach analyte individually.

Results

Synthesis of Free L-Fucose by the E. coli BL21(DE3) Production StrainExpressing a Fucosyltransferase Gene

To enhance GDP-L-fucose synthesis in E. coli BL21(DE3) heterologousgenes encoding phosphomannomutase, mannose-1-phosphateguanosyltransferase, GDP-mannose-4,6-dehydratase, and GDP-L-fucosesynthase were genomically integrated and overexpressed. Additionally, toconfer to the BL21(DE3) strain the ability to grow on sucrose, thecsc-gene cluster, encoding sucrose permease, fructokinase, sucrosehydrolase and a transcriptional repressor, from E. coli W was integratedin the genome.

The 2-fucosyltransferase WbgL catalyzes the transfer of L-fucose fromthe donor molecule GDP-L-fucose to an acceptor oligosaccharide. However,in the absence of an acceptor molecule free L-fucose could be detectedin the supernatant of the bacterial cultures, when growing the E. coliBL21(DE3) production strain harboring pDEST:wbgL in an appropriatemedium. Free L-fucose is released from GDP-fucose by the GDP-L-fucosehydrolase activity of WbgL.

To further improve the GDP-L-fucose hydrolase activity of WbgL the wbgLgene was subjected to random mutagenesis using error-prone PCR. Alibrary of about 5000 E. coli BL21(DE3) production strains harboringpDEST:wbgL(error-prone) clones was tested for improved GDP-L-fucosehydrolase activity. Two clones (designated as clones D1 and H2) showedincreased production of free L-fucose, as determined by analysis ofculture supernatants using the L-fucose dehydrogenase assay (FIG. 1).Two amino acid substitutions were found in the WbgL sequence of each ofthe two clones. The WbgL variant of clone D1 contained amino acidsubstitutions histidine 124 to alanine and glutamate 215 to glycine, inthe WbgL variant of clone H2 residue asparagin 69 was exchanged toserine and isoleucine 268 to proline.

Supernatants of the E. coli BL21(DE3) production strain harboringplasmids pDEST:wbgL, pDEST:wbgL(H124A E215G) D1 and pDEST:wbgL(N69SI268P) H2 were also subjected to LC-MS/MS analysis. L-fucose wasidentified by MRM analysis in each sample. The amount of free L-fucosewas determined using maltotriose as an internal standard fornormalization. For the strain expressing the wbgL wild-type gene 0.12g/L L-fucose were determined in the culture supernatant. Hydrolyticactivity of WbgL variants (H124A, E215G), and (N69S, I268P) was clearlyincreased. Clones D1 and H2 produced 0.43 g/L and 0.25 g/L L-fucose,respectively (FIG. 2).

Detection of GDP-L-Fucose Hydrolase Activity in Cell Lysates ofMicroorganisms Expressing Fucosyltransferase Genes

GDP-L-fucose hydrolase activity was analyzed in cell free extracts of E.coli BL21(DE3) pDEST:wbgL (H124A E215G) and E. coli BL21(DE3)pDEST:futC, grown in the presence of the transcriptional inducer IPTG.The 2-fucosyltransferase FutC is described to hydrolyze GDP-L-fucose inthe absence of an oligosaccharide substrate (Stein, D. B., Lin Y.-N.,Lin, C.-H. (2008) Characterization of Helicobacter pyloriα1,2-fucosyltransferase for enzymatic synthesis of tumor-associatedantigens. Adv. Synth. Catal. 350, 2313-2321). GDP-L-fucose was cleavedin the hydrolase assay that contained 5 mM GDP-L-fucose and cell lysatesof the respective strains. Using the L-fucose dehydrogenase assay freeL-fucose was detected. No free L-fucose was detected in the assaycontaining bovine serum albumin instead of crude extract, demonstratingstability of GDP-L-fucose (FIG. 3).

For quantification of the L-fucose released by in vitro hydrolyses ofGDPL-fucose the hydrolase assays were cleared by solid phase extractionusing ion exchange cartridges (Strata ABW, Phenomenex, Aschaffenburg,Germany) and analyzed by LCMS/MS. In assays containing cell lysates ofthe futC, and wbgL(H124A E215G) expressing strains, 0.38 g/L and 0.32g/L L-fucose, respectively, were measured after 1 hour incubation,corresponding to specific GDP-L-fucose hydrolase activities of 0.18 U/mgfor FutC and 0.21 U/mg for WbgL (H124A E215G).

1. Process for producing a monosaccharide of interest in free form usinga microorganism, the process comprising a.) providing a microorganismfor the synthesis of the monosaccharide comprising an enzyme capable ofcatalyzing the hydrolysis of a nucleotide-activated monosaccharide torelease the monosaccharide of interest from the nucleotide-activatedmonosaccharide, and b.) cultivating the microorganism in a mediumsuitable for growing the microorganism, wherein the microorganism isunable to metabolize the monosaccharide to a significant extent, so thatthe monosaccharide of interest accumulates during cultivation.
 2. Theprocess of claim 1, wherein a recombinant microorganism is used, whereinthe recombinant microorganism comprises a heterologous nucleic acidencoding an enzyme capable of catalyzing the hydrolysis of anucleotide-activated monosaccharide.
 3. The process of claim 1, whereinthe enzyme is a glycosyltransferase, optionally a fucosyltransferase,the enzyme being able to catalyze the hydrolysis of thenucleotide-activated monosaccharide GDP-fucose in the absence of anacceptor molecule.
 4. The process of claim 1, wherein the enzyme is avariant of the 2-fucosyltransferase encoded by the wbgL gene fromEscherichia coli, or a variant of the 1,2-fucosyltransferase encoded bythe futC gene from Helicobacter pylori, the variant carrying at leastone, optionally at least two, and optionally more than two modificationsas compared to the wild type 2-fucosyltransferase encoded by the wbgLgene or to the wild type 1,2-fucosyltransferase encoded by the futCgene, respectively, the modification leading to an increased hydrolizingactivity of the enzyme.
 5. The process of claim 4, wherein at least onemodification is an amino acid substitution.
 6. The process of claim 1,wherein the microorganism is further modified to have inactivated orseverely reduced or to lack catabolic pathways leading to thedegradation of the produced monosaccharide.
 7. The process of claim 1,wherein the microorganism is further modified to have inactivated orseverely reduced or to lack genes involved in the catabolism ofL-fucose.
 8. The process of claim 1, wherein the microorganism isfurther modified to overexpress at least one gene involved in thebiosynthesis of the nucleotide-activated monosaccharide to improvesupply of the nucleotide-activated monosaccharide of the monosaccharide.9. The process of claim 1, wherein at least one gene involved in thebiosynthesis of GDP-fucose, GDP-mannose or GDP-rhamnose is overexpressedto improve supply of GDP-fucose, GDP-mannose or GDP-rhamnose,respectively.
 10. The process of claim 8, wherein the at least one geneis heterologous or homologous.
 11. The process of claim 1, wherein themicroorganism is further modified to have inactivated or reducedcompeting pathways for the nucleotide-activated monosaccharide.
 12. Theprocess of claim 1, wherein the monosaccharide produced is selected fromL-fucose, L-rhamnose, or L-mannose.
 13. The process of claim 1, whereinthe microorganism is cultivated in a medium containing an inexpensivecarbon source that is selected but not limited to glycerol, sucrose,glucose, fructose, molasse, xylose, cellulose, syngas, corn-syrup orlactose.
 14. The process of claim 1, wherein the microorganism isfurther modified to express a phosphatase, in case where themonosaccharide is released in a phosphorylated form by the enzyme. 15.Recombinant microorganism comprising a heterologous enzyme capable ofcatalyzing the hydrolysis of a nucleotide-activated monosaccharide andreleasing the monosaccharide from the nucleotide-activatedmonosaccharide in the absence of an acceptor molecule, wherein theenzyme is a glycosyltransferase, optionally a fucosyltransferase. 16.The recombinant microorganism of claim 15, wherein the enzyme is avariant of the 2-fucosyltransferase encoded by the wbgL gene, or avariant of the 1,2-fucosyltransferase encoded by the futC gene fromHelicobacter pylori, the variant carrying at least one, optionally atleast two, and optionally more than two modifications as compared to thewild type 2-fucosyltransferase encoded by the wbgL gene or to the wildtype 1,2-fucosyltransferase encoded by the futC gene, respectively, themodification leading to an increased hydrolizing activity of the enzyme.17. The recombinant microorganism of claim 15, that is further modifiedto comprise heterologous genes encoding phosphomannomutase,mannose-1-phosphate guanosyltransferase, GDP-mannose-4,6-dehydratase,and GDP-L-fucose synthase.
 18. The process of claim 1, wherein orrecombinant host microorganism produced therefrom wherein the hostmicroorganism is an Escherichia coli strain, Corynebacterium spp.,Clostridium spp., Bacillus spp. Pseudomonas spp. Lactobacillus spp. or aSaccharomyces sp. strain.